1. Technical Field
The disclosure relates in general to a stacked-type piezoelectric device and a method for manufacturing the same, and more particularly to a stacked-type piezoelectric device capable of reducing damage and the volume and a method for manufacturing the same.
2. Description of the Related Art
Piezoelectric material has an asymmetric center in the crystal phase, which results in uneven charge distribution. After polarization treatment, the inputted voltage is converted into mechanical displacement or deformation which generates electric current. When the inputted voltage is alternative current, the material vibrates correspondingly and generates vibration waves. On the contrary, when the piezoelectric membrane is pressed which generates deformation potential energy, the potential energy is converted into electric energy at the moment of release.
Due to the special characteristics of the material, the piezoelectric material is suitable for being applied to many devices in people's daily lives, for energy saving and environmental protection. For example, when the piezoelectric device is applied to the lens of a compact electronic product, such as the lens of a camera phone, a constant voltage can be applied to the piezoelectric device under the lens for causing constant expansion, which drives the lens to perform the focus adjustment. When the piezoelectric device is applied to an ultrasonic nebulizer, the piezoelectric ceramic membrane generates high-frequency vibration waves, which break up water into extremely fine mist droplets and sends the mist droplets to the air through the high-frequency vibration principle of the piezoelectric effect. Furthermore, through the piezoelectric effect, the deformed piezoelectric material is able to generate electric current. For example, the piezoelectric device is placed in the shock absorbent material in the automobile engine. When the engine vibrates, the piezoelectric device is deformed which generates electric current. As a result, part of the energy is recycled to save energy. Other examples include consumer products and industrial supplies, such as the ink droplet control in the inkjet printer, ultrasonic medical image, nondestructive testing for detecting the internal defects within the structure . . . etc. However, most of the piezoelectric devices are made of several sheets of stacked piezoelectric materials for higher driving deformation or greater electric current. The reasons include: (1) the deformation of the piezoelectric materials is nonlinear, so it is easier to control the deformation when the piezoelectric materials are stacked together; and (2) less driving current is needed, which obtains better frequency response.
Please refer to FIG. 1. FIG. 1 illustrates a stacked-type piezoelectric actuator. Several vertically-stacked piezoelectric layers 2 are electrically connected to each other and electrically conducted through two lateral sides. When a low voltage is applied for driving the device, those piezoelectric layers 2 are deformed. As a result, the entire height of the piezo stack increases to (L+ΔL) from the original stacking height L.
Conventionally, when the stacked-type piezoelectric device is in use, a conductive surrounding structure or a frame which functions as a casing is required to fasten the piezoelectric materials. Please refer to FIG. 2, which illustrates the structure of a conventional piezoelectric actuator. The piezoelectric actuator includes several vertically-stacked piezoelectric layers 2, an electrode layers 3 disposed between the piezoelectric layers 2, a frame 4 to fasten the piezoelectric layers 2 and a contact layer 5 to conduct electricity to the electrode layers 3. The frame 4 is connected to the lateral sides of the piezoelectric layers 2 and electrically connected to an external connector 6 through a copper wire 7. As shown in FIG. 2, an operating voltage is applied to the connector 6, and the right half and the left half of the frame 4 are connected to the positive and negative electrodes respectively. As a result, the even-numbered and odd-numbered layers of the electrode layers 3 which are counted from the top carry positive and negative charge respectively. An electric field is generated correspondingly in the center region M where electrode layers 3 overlap. Accordingly, the piezoelectric layers 2 corresponding to the center region M deform and expand. The expanding direction is indicated by the arrows. The portion of the piezoelectric layers 2 corresponding to the edge region R expands less because there is no electric field effect there. Lateral ends of the piezoelectric layers 2 do not deform because being restrained by the frame 4.
However, the conventional piezoelectric actuator has some disadvantages when in practical use. The lateral ends of the piezoelectric layers 2 are fastened by the frame 4. When the central portion of the piezoelectric layers 2 deform, the total height of the lateral sides remains the same. Therefore, tensile stress exists at the boundary between the central portion and the rim of the piezoelectric layers 2, which causes extremely uneven stress distribution. When the deformation is greater, the tensile stress becomes higher, which leads to fracture easily. Furthermore, only part of the piezoelectric layers 2 which corresponds to the center region M is deformed effectively. In the edge region R where the electrodes do not overlap cannot effectively perform piezoelectric effect. Moreover, the frame 4 used for fastening the stacked piezoelectric layers 2 increases the entire volume of the piezoelectric actuator, and the piezoelectric actuator becomes heavier accordingly.